Air fresheners come in a variety of types. Sprays which release the fragrance in gaseous form provide a quick result, but the effect is not enduring because the fragrance vapors quickly dissipate. Consequently, frequent reapplication is necessary.
To overcome this problem, devices have been introduced which provide for the constant or intermittent emission of fragrance. One means of accomplishing gradual emission of an air freshening scent is to expose the fragrance in semi-solid or liquid form to the atmosphere, resulting in gradual vaporization of the solid or liquid material. This vaporization process may be accelerated by the use of heat.
Desirable characteristics of any air freshening device designed for gradual emission include an attractive physical appearance and an even rate of discharge of the fragrance, so that the scent is neither overpowering nor absent at any time. Ideally, the device should dispense the fragrance at a substantially constant rate over the useful life of the product.
Another beneficial feature of an ideal air freshener would include a container that could be refilled with fragrance so that reuse would be possible instead of disposal. Additionally, the container should be able to adequately hold and contain the air freshening agent and thereby prevent contact with, and potential damage to, surrounding surfaces. Another positive attribute would be low cost to the consumer over the life of the product. An ideal reusable air freshener should also have a method of clearly indicating to the user when more air freshener is needed.
Plastic disposable air fresheners have traditionally dominated the market for continuous-action air freshening devices. The advantage of plastic dispensers is that they are inexpensive to manufacture and package and are consequently less costly in initial cash outlay to the consumer. Because of such low initial cost, such dispensers are generally designed to be replaced rather than refilled when the freshening agent has completely vaporized.
A distinct disadvantage of plastic containers is that such containers are not generally reusable since many of these containers are not designed to be refillable. This disposable aspect of plastic air fresheners raises certain environmental concerns, since many plastics are not biodegradable and must take up valuable landfill space.
Furthermore, such products, because they tend to be inexpensively made, may not be particularly attractive in appearance. The plastic container also does not serve a purpose in the task of accomplishing air freshening, other than to act as a mere container to hold the fragrance agent. An additional disadvantage is that most of these containers have openings in the plastic to allow for the emission of vapors from the container, making accidental contact between the fragrance agent and a surface material more likely. Such contact could cause permanent damage to a table surface or to clothing.
Wooden containers providing for the emission of vapors having an insect repellent purpose are disclosed by the prior art. U.S. Pat. No. 2,218,037 (Duers) teaches the use of a small cedar device into which is inserted a fabric plug soaked in insect repellent and held in place in the interior of the device by a wooden plug. The Duers device is then covered with a permeable coating such as paraffin, which serves to meter the emission of insect repellent vapors. Alternatively, the interior is filled with a paraffin-repellent plug, the paraffin again serving a metering function. In both forms, the Duers patent teaches that the interior of the device holds the repellent during the period of emission from the device. The device is designed to be used where fabric materials are stored to prevent insect damage to clothing. There is no teaching with respect to air freshening dispensers, and no teaching of the use of wood for holding/metering purposes.
The prior art also discloses that oils or other liquids will tend to migrate into and along a piece of wood by means of the capillaries in the wood grain. U.S. Pat. No. 2,241,167 (Storck) discloses this principle in connection with the absorbance of insect repellant by a wooden egg-shaped piece of cedar. The Storck device is also used to protect clothing from moth or other insect damage. It has no teachings with respect to air freshener devices.
Among the many continuous-action air freshener devices of the prior art are ceramic bowls. Some liquid air freshener is poured into each bowl through a top opening, which is then covered. The liquid gradually passes through the ceramic from the pool in the bowl and is evaporated at the surface of the bowl. The bowl has a relatively thin wall and encloses a large central chamber.
One problem with many types of continuous-action air freshener devices of the prior art is that it may be difficult to determine when the useful life of the product has ended. Usefulness often fades away with no readily perceptible sign.